Variable speed compressor cooling system

ABSTRACT

A compressor assembly including one or more compressors associated with compressor drive means. A cooling system is positioned downstream from the compressor and includes at least one air circulator, for example, a fan or a blower, and at least one heat exchanger. The air circulator is associated with a circulator variable speed drive, the speed of which can be adjusted independent of the compressor drive means. One or more sensors are associated with the circulator drive. The sensors sense desired variables and the speed of the circulator drive is adjustable in response to real-time sensed conditions.

BACKGROUND

[0001] The present invention relates to compressors. More particularly,the present invention relates to cooling systems for compressors.

[0002] There are two principle designs of compressors, contact cooledand oil free. Contact cooled compressors are generally defined ascompressors that inject coolant into the compression chamber tolubricate, remove the heat of compression, and seal the clearancesbetween the compressor rotors. Oil free compressors are generallydefined as compressors that separate the air and oil systems, ifrequired, to prevent contamination of the compressed air. In both cases,the air and oil or coolant must be cooled to remove the heat ofcompression and heat from friction.

[0003] Air-cooled air compressors remove the heat from the air and oilby using fans or blowers to force or draw air through a heat exchangeror combination of heat exchangers. Typically, air-cooled cooling systemsare sized by matching the fan or blower with a heat exchanger to meetthe Limiting Ambient Temperature (LAT) and Cold Air TemperatureDifference (CTD) requirements for the compressor. The LAT is defined asthe maximum ambient temperature the compressor will operate. The CTD isdefined as the difference between the compressed air dischargetemperature and the ambient air temperature. The LAT and CTDrequirements are fixed values based on predicted values. The predictedvalues are typically chosen to correspond to worst case scenarios. Inmost applications, the compressor does not operate in the worst caseconditions.

[0004] Current cooling systems incorporate one of two methods ofcontrolling fans or blowers: (1) fixed speed operation and (2) variablespeed operation. In the fixed speed designs, the speed of the fan orblower remains constant regardless of the operation of the compressor orthe ambient conditions or customer's requirements. In the currentvariable speed applications, a single variable frequency drive (VFD) isused to control the speed of the compressor and fan or blower. Thismethod of variable speed control requires the speed of the fan or blowerto be adjusted linearly with the speed of the compressor.

[0005] Neither of the two current fan and blower control methodsprovides the customer an optimized cooling system for any givenapplication.

SUMMARY

[0006] The present invention relates to a compressor assembly. Thecompressor assembly includes one or more compressors associated withcompressor drive means. The compressor drive means may include constantspeed drives or variable speed drives. A cooling system is positioneddownstream from the compressor and includes at least one air circulator,for example, a fan or a blower, and at least one heat exchanger. The aircirculator is associated with a variable speed circulator drive means,for example, a variable speed motor, the speed of which can be adjustedindependent of the compressor drive means. One or more sensors areassociated with the circulator drive means. The sensors sense desiredvariables, for example, ambient temperature, airend dischargetemperature, coolant injection temperature, package dischargetemperature, compressor drive means speed, dryer inlet temperature,compressor point of use temperature or airend discharge pressure. Thespeed of the circulator drive means is adjustable in response toreal-time sensed conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a schematic flow diagram of a compressor assemblyaccording to a first embodiment of the present invention.

[0008]FIG. 2 is a schematic flow diagram of a compressor assemblyaccording to a second embodiment of the present invention.

[0009]FIG. 3 is a schematic flow diagram of a compressor assemblyaccording to a third embodiment of the present invention.

[0010]FIG. 4 is a schematic flow diagram of a compressor assemblyaccording to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described with reference to theaccompanying drawing figures wherein like numbers represent likeelements throughout. Certain terminology, for example, “top”, “bottom”,“right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and“rearward”, is used in the following description for relativedescriptive clarity only and is not intended to be limiting.

[0012] Referring to FIG. 1, a compressor assembly 10 that is a firstembodiment of the present invention is shown. The compressor assembly 10provides compressed fluid, preferably air, to downstream components viaan outlet 28. The downstream components (not shown) may be any ofvarious devices, for example, further conditioning components likedryers, filters and the like, intermediate storage tanks, or end usertools, motors or the like.

[0013] The compressor assembly 10 generally comprises a compressor 2having an air inlet 4 and an air outlet 6. The compressor 2 can havevarious configurations, for example, it may be a conventionalsingle-stage reciprocating compressor, a dual-stage reciprocatingcompressor, a rotary screw compressor, a centrifugal compressor, or ascroll compressor among others. The compressor 2 may be contact cooledor oil free.

[0014] The compressor 2 is driven by a compressor drive 3. Thecompressor drive 3 may be a conventional electric motor or a combustionengine amongst others. The compressor drive 3 may be constant speeddrive or alternatively may be a variable speed drive (“VSD”).

[0015] Air, or another intended fluid, enters the compressor 2 throughthe inlet 4 and is compressed to a desired pressure. The compressedfluid exits the compressor 2 through the fluid outlet 6 and travels to adownstream cooling system 8. The cooling system 8 generally comprises aheat exchanger 12 and an air circulator 14, for example a fan or ablower, for drawing or forcing air across the heat exchanger 12. The aircirculator 14 is driven by a variable speed drive (“VSD”) 16 associatedtherewith. The VSD 16 preferably comprises a variable speed frequencydrive and an electric motor. The compressed fluid travels through thecooling system 8 and the cooled, compressed fluid travels to thedownstream components via the outlet 28. In addition to cooling thecompressed fluid, the cooling system 8 may be utilized to cool thecooling fluid circulating through the compressor 2. A fluid loop (seeFIG. 4) for carrying the cooling fluid from the compressor 2 to thecooling system 8 may be provided.

[0016] To achieve a desired condition of the compressed fluid, the aircirculator VSD 16 is associated with at least one sensor 18 or othermeasuring device. The sensor 18 may provide sensed information tocontroller 20, for example, a CPU, which in turn provides a controlsignal to the air circulator VSD 16. Alternatively, the sensor 18 mayprovide sensed information directly to the air circulator VSD 16, asindicated by line 26 in FIG. 1. The air circulator VSD 16 would vary itsspeed in direct response to the sensed information. Communicationbetween the sensor 18, controller 20 and air circulator VSD 16 may betransmitted through hard wiring or through wireless technology, forexample, RF transmission, or a combination thereof. In response to thesensed information, the air circulator VSD 16 speed may be variedelectronically and/or mechanically.

[0017] In the compressor assembly 10 illustrated in FIG. 1, the sensor18 is a temperature sensor that is positioned between the compressoroutlet 6 and the cooling system 8. The sensor 18 senses the temperatureof the compressed fluid exiting the compressor 2 and provides,preferably continuously, such information to the controller 20 ordirectly to the air circulator VSD 16. The sensor 18 for sensingtemperature can be an RTD (Resistance Temperature Detector),thermocouple, thermistor or other electrical device capable oftranslating a temperature within a predefined range into a varyingpotential or current, or, a filled-system device containing mercury orother temperature sensitive fluid. The temperature element can bemounted using a thermowell (not shown) or nude within the compressordischarge piping 6. The sensor 18 continuously measures the dischargegas temperature. A temperature measurement signal corresponding to thedischarge gas temperature is provided to the controller 20. Thecontroller 20 can accept a current, voltage or filled-system processvariable input.

[0018] As such, the speed of the air circulator 14 can be adjusted inresponse to the real-time information provided by the sensor 18. Forexample, if the temperature of the compressed fluid increases, the aircirculator VSD 16 is sped up such that the air circulator 14 draws orforces more air across the heat exchanger 12 to effect greater cooling.

[0019] Referring to FIG. 2, a compressor assembly 60 that is a secondembodiment of the present invention is shown. The compressor assembly 60is substantially the same as in the previous embodiment and likecomponents have like numerals. In this embodiment, the sensor 18 isprovided at the downstream outlet 28. The sensor 18 measures thetemperature of the compressed fluid as it exits the cooling system 18.The air circulator VSD 16 may be controlled in response to this singlevariable. However, in the present embodiment, a second sensor 30 isassociated with the controller 20. The second sensor 30 senses theambient air temperature. The controller 20 can compare the sensedtemperature of the compressed fluid (sensor 18) with the sensed ambienttemperature (sensor 30) to determine the CTD. The air circulator VSD 16can then be controlled to maintain the CTD within a desired range.

[0020] Referring to FIG. 3, a compressor assembly 70 that is a thirdembodiment of the present invention is shown. The compressor assembly 70is similar to the previous embodiments and the like components have likenumerals. The compressor assembly 70 has a pair of compressors 2, 2′ anda pair of cooling systems 8, 8′. Each compressor 2, 2′ has its owncompressor drive 3, 3′, respectively. Alternatively, a single drive maybe utilized to drive both compressors 2, 2′. Each cooling system 8, 8′is also shown with its own air circulator VSD 16, 16′, respectively.While a single drive may be utilized with both cooling systems 8, 8′, itis preferred that each cooling system 8, 8′ be provided with its own VSD16, 16′. The compressors 2, 2′ are shown in parallel, but may beconnected in series or in any other desired configuration. In theillustrated configuration, fluid travels from each inlet 4, 4′; throughcompressors 2, 2′ to outlets 6, 6′, respectively; through coolingsystems 8, 8′ and outlets 28, 28′, respectively, to a common outlet 40and through dryer 42 to outlet 48. Outlet 48 connects to desireddownstream components. The dryer 42 may be a refrigeration type dryer ora desiccant type dryer amongst others.

[0021] A plurality of sensors 18, 36, 38, 44, 46, 50 and 52 arepositioned along the system to read various conditions. In theillustrated embodiment, the sensors sense the following information:sensor 18 sensors the temperature of the compressed fluid dischargedfrom cooling system 8; sensor 36 senses the temperature of thecompressed fluid discharged from the cooling system 8′; sensor 38 sensesthe pressure of the compressed fluid traveling through the common outlet40; sensor 44 senses the temperature of the compressed fluid at thedryer 42 inlet; sensor 46 senses the temperature of the dryer cold airwell; sensor 50 senses the temperature of the compressed fluiddischarged from the dryer 42; and sensor 52 senses the ambienttemperature. The number, type and positioning of the sensors may bevaried.

[0022] All of the sensed information is provided to controller 20. Thecontroller 20 also receives feedback from each of the drives 3, 3′, 16,16′, for example, drive speed. The controller 20 gathers the rawinformation and may also configure and compare the information. Forexample, the controller 20 may use the sensed outlet pressure (sensor38) to determine the pressure dew point at that point of the system. Thepressure dew point may be compared with the compressed fluid temperaturefrom each compressor 2,2′ (sensors 18, 36) and determine if any systemadjustment is required. As another example, the controller may configurethe readings of the various dryer sensors 44, 46, 50 and compare suchinformation to the known ideal operating conditions of the dryer 42. Thecontroller 20 continuously monitors and configures the data from anydesired combination of the sensors 18, 36, 38, 44, 46, 50 and 52 andadjusts the air circulator VSDs 16, 16′ to optimize the operatingconditions of the compressor assembly 70. For example, the coolingsystem 8 may be sped up while the cooling system 8′ is slowed down toprovide a desired compressed fluid temperature (sensor 44) entering thedryer 42.

[0023] Referring to FIG. 4, a compressor assembly 80 that is a fourthembodiment of the present invention is shown. The compressor assembly 80is substantially the same as in the previous embodiments and likecomponents have like numerals. In this embodiment, the compressor 2 isan oil flooded compressor. The sensor 18 is positioned at the dischargeoutlet 6 of the compressor 2, and is preferably configured to measurethe temperature of the discharged air/oil mixture. The air/oil mixturepasses to a separator tank 82 where the oil is separated from thecompressed air. Fluid conduit 84 carries the compressed air to thecooling system 8 and a fluid conduit 86 carries the separated oil to thecooling system 8. The compressed air passes through the cooling system 8and travels to the downstream components via the outlet 28. Theseparated oil passes through the cooling system 8 and is redirectedthrough conduit 88 back to the compressor oil inlet 5. A valve 90 ispreferably provided along the fluid conduit 88 and is communication withthe controller 20. The controller 20 is configured to control the valve90, and thereby regulate the amount of oil injected into the compressor2, based on the various sensed parameters. In the illustratedembodiment, the sensed parameter is the temperature of the air/oilmixture at the compressor outlet 6. As such, the controller can controlthe temperature of both the compressed air and of the separated oil bycontrolling the cooling system VSD 16. Additionally, the amount of oilinjected in to the compressor 2 can also be controlled to assist inmaintaining the discharge temperature of the air/oil mixture within adesired range.

[0024] The above described embodiments are illustrative only and are notintended to be limiting. Other variations of the present invention willfall within the scope of this invention. Other components and devicesmay be positioned in the compressor assembly circuits and the relativeposition of the illustrated components may be varied.

What is claimed is:
 1. A compressor assembly comprising: a compressorassociated with a compressor drive means; a cooling system positioneddownstream from the compressor and configured to receive compressedfluid discharged from the compressor, the cooling system comprising: aheat exchanger; an air circulator configured for moving air across theheat exchanger; and a variable speed circulator drive means operatingindependently of the compressor drive means; and at least one sensor,configured to sense at least one characteristic of the compressed fluid,associated with the circulator drive means such that the speed of thecirculator drive means is adjusted in response to a real-timecharacteristic sensed by the at least one sensor.
 2. The compressorassembly of claim 1 wherein the circulator drive means comprises avariable speed frequency drive and an electric motor.
 3. The compressorassembly of claim 1 wherein the at least one sensor is a temperaturesensor configured to measure the temperature of the compressed fluid. 4.The compressor assembly of claim 3 wherein the at least one sensor ispositioned between the compressor and the cooling system.
 5. Thecompressor assembly of claim 3 wherein the at least one sensor ispositioned downstream from the cooling system.
 6. The compressorassembly of claim 3 wherein the at least one sensor and the circulatordrive means are associated with a controller configured to send acontrol signal to the circulator drive means based on received signalsfrom the at least one sensor.
 7. The compressor assembly of claim 6further comprising a secondary sensor associated with the controller andconfigured to measure an ambient temperature.
 8. The compressor assemblyof claim 6 further comprising a secondary sensor associated with thecontroller and configured to measure compressor drive means speed. 9.The compressor assembly of claim 6 further comprising a secondary sensorassociated with the controller and configured to measure compressordischarge pressure.
 10. The compressor assembly of claim 6 wherein thefluid discharged from the compressor is separated in a separator tank into compressed fluid and separated lubricant and wherein the compressedfluid is directed through the cooling system and the separated lubricantis directed back to the compressor via a lubricant conduit.
 11. Thecompressor assembly of claim 10 wherein the separated lubricant isdirected through the cooling system before returning to the compressor.12. The compressor assembly of claim 10 further comprising a valvepositioned along the lubricant conduit to control the amount ofseparated lubricant entering the compressor.
 13. The compressor assemblyof claim 12 wherein the valve is associated with the controller and theamount of separated lubricant entering the compressor is controlled bythe controller based on received signals from the at least one sensor.14. The compressor assembly of claim 6 wherein the fluid discharged fromthe compressor is directed to a dryer.
 15. The compressor assembly ofclaim 14 further comprising a secondary sensor associated with thecontroller and configured to sense at least one characteristic of thecompressed fluid at an inlet to the dryer.
 16. The compressor assemblyof claim 15 wherein the at least one characteristic of the compressedfluid at the inlet to the dryer is one of the compressed fluidtemperature, relative humidity or due point.
 17. The compressor assemblyof claim 14 further comprising a secondary sensor associated with thecontroller and configured to sense at least one characteristic of thecompressed fluid at an outlet to the dryer.
 18. The compressor assemblyof claim 17 wherein the at least one characteristic of the compressedfluid at the outlet to the dryer is one of the compressed fluidtemperature, relative humidity or due point.
 19. The compressor assemblyof claim 1 further comprising a secondary compressor and a secondarycooling system positioned downstream from the secondary compressor andconfigured to receive compressed fluid discharged from the secondarycompressor, the secondary cooling system comprising: a secondary heatexchanger; a secondary air circulator configured for moving air acrossthe heat exchanger; and a secondary variable speed circulator drivemeans configured to operate independently from the circulator drivemeans.
 20. The compressor assembly of claim 19 wherein a secondarysensor is associated with the secondary circulator drive means.
 21. Thecompressor assembly of claim 20 further comprising a controllerassociated with the at least one sensor, the secondary sensor, thecirculator drive means and the secondary circulator drive means, thecontroller configured to independently control the circulator drivemeans and the secondary circulator drive means based on signals receivedfrom the at least one sensor and the secondary sensor.
 22. Thecompressor assembly of claim 1 wherein the at least one characteristicof the compressed fluid sensed by the at least one sensor is one of thecompressed fluid temperature, relative humidity, due point, orcompressed fluid pressure.